1. Field of the Invention
This invention relates to a lap-top type personal computer in which an extended memory can be additionally installed, and more particularly, to a lap-top type personal computer for accessing two types of extended memories having different memory capacities, by using identification information set in a register.
2. Description of the Related Art
Recently, so-called lap-top type personal computers have been variously developed as portable type personal computers. This type of personal computer has a connector for connecting an extended memory to the main body of the personal computer in order to enhance the data processing ability thereof. For example, extended memories having a memory capacity of 2 megabytes or 4 megabytes are frequently used as extended memories. In a case where such an extended memory is connected to the connector of a lap-top type personal computer, the internal memory of the personal computer, originally having a memory capacity of 1 megabyte, for example, can be extended to have a memory capacity of 3 or 5 megabytes. Therefore, if the extended memory is used, the user can extend the internal memory capacity of his or her personal computer to a desired memory capacity according to the desired application of the lap-top type personal computer.
However, in order to simplify the address assignment with respect to the extended memory in a normal lap-top type personal computer, the types or the memory capacities of extended memories which can be connected to respective connectors must be determined. That is, an exclusive connector for a 2-megabyte extended memory and an exclusive connector for a 4-megabyte extended memory are separately provided for the personal computer. It is required to connect a 2-megabyte extended memory to a corresponding exclusive connector and a 4-megabyte extended memory to another corresponding exclusive connector. Therefore, when the user connects an extended memory to the lap-top type personal computer, he or she is required to confirm the type of connector or that the connector is a 2-megabyte type or 4-megabyte type before the extended memory is actually connected to the connector, which makes the memory extending operation troublesome.
Further, in a normal lap-top type personal computer, when two or more extended memories are additionally installed, the extended memories must be sequentially connected to the respective connectors so as not to provide an unused connector between any two connectors which are to be used. That is, in a case where two extended memories are additionally installed in the personal computer having three connectors or first to third connectors to which priority levels are assigned in that order, the two extended memories must be connected to the first and second connectors. This is because an address space which follows an address space assigned to the first connector is assigned to the second connector, an address space which follows the address space assigned to the second connector is assigned to the third connector, and if the two extended memories are connected to the first and third connectors without using the second connector, then the address spaces assigned to the two extended memories become discontinuous.
In this way, in the prior art, the memory of a lap-top type personal computer can be extended only in a restricted condition and their is little freedom in extending the memory capacity thereof.